I believe this might be one part of the I/O solution:
http://superuser.com/questions/67659...rk/70657#70657
I guess the mouse could be forwarded just the same way the keyboard is forwarded there. The rest is simple X-forwarding.

However, this would require to set up an actual network connection between the two devices, not just a mass storage connection. I'm sure that's possible via USB somehow (I haven't checked). Edit: We have everything in house: http://wiki.maemo.org/N900_USB_networking /Edit

Any other interfaces wouldn't be really useful since all of them (Bluetooth, IrDA and (W)LAN) require additional hardware.

It would also require to intercept the inputs that are intended for the Raspberry before they accidentally do any funny things on the N900. But I guess that's no real issue. We'd need an extra application (that grabs all the inputs) anyway to control the Raspberry desktop since we need a mouse and the first thing that comes into mind is to use the N900's screen as a touchpad.


another idea:
The Raspberry PI model B comes with 256MB of RAM. A minimal Debian with X-Server and a lightweight WM (opebox, fluxbox, icewm etc) would leave us approximately 200MB of free memory. Assuming that we don't stream any data to our Raspberry that gives us additional 200MB of RAM connected via a 20-25MB/s USB interface. No idea if that would actually be faster than the swap partition when routed via an additional TCP interface and it should certainly be used with a lot of caution but I think it's worth a try.